Pneumatic power tools with specialized consumables are used by operator persons in many different industries to accomplish specific tasks such as dimensioning, defect removal, deburring, blending, finishing, corrosion removal, cleaning, polishing, surface preparation and many more.
In most industries and particularly in the aerospace and automotive industries, the proper control over the parameters of such processes has a large impact on the quality of the work performed. Unfortunately, optimum parameters are seldom available to the operator person using the hand held power tool.
For example, the rotational speed at which the consumable is used has a direct impact on its performance and wear. This is true for most consumables such as, but not limited to discs, sanding bands, grinding wheels, drill bits, rotary cutters and bristle disks. The problem is that the operator person is often unaware of the optimal speed for the consumable. Furthermore, he often only has a single power tool to work with and has a tendency of running at the maximum speed for the power tool even if this maximum speed is much higher than the optimal speed for the consumable. It is possible to calculate the optimal speed for a consumable but the calculation is mathematically complex and requires data and parameters not typically accessible to the operator person.
The use of consumables at inadequate speeds has led to numerous injuries to operator persons when the consumable breaks down or detaches from the spindle and hits the body of the operator person or someone nearby. Furthermore, using consumables at inadequate speeds often leads to the rapid wear of the consumable which significantly increases the cost of the process. Additionally, inadequate rotational speed can damage the part being treated by causing excessive heat or abrasion. This may lead to the replacement of the part further increasing the cost of the process by several orders of magnitude.
For example, hand held power tools are used to remove old sealant and adhesive on aircraft panels. During the maintenance and overhaul of aircraft, panels must be removed to access maintenance areas. The panel's joints and fasteners are often covered with sealant to avoid water infiltration. This old sealant can be removed with rotary cutters and bristle disks. These two types of consumables run at very different speeds usually with different hand held power tools. Most companies do not equip their operators with many different tools in the same family of pneumatic tool, to reduce operational cost. When the wrong power tool is used and/or the wrong speed selected, the rotary cutters made of hard plastic can quickly disintegrate and damage the underlying base material like paints, primers, alodine, and metal. The bristle disks, made of soft plastic, tend to disintegrate when used at higher speeds than indicated. In both cases, the cost of using the wrong rotational speed for the job can be very high.
Many drill bits use special coatings or material to extend their performance and useful life. When the rotational speed of the drill bit is too high, excessive heat is produced by the drilling which quickly burns the tip of the drill bit making it ineffective. The use of the optimal rotational speed for the drill bit size will make drill bits more effective and longer lasting.
The removal of scratches, dents and corrosion on aircraft structure using abrasive wheels and disks would also greatly benefit from optimal controlled rotational speed. When the optimum speed is not used, abrasive wheels and disks can quickly bring the component thickness below its acceptable minimum limit. Furthermore, the wrong speeds can generate heat on the surface thus modifying the heat treatment of the part. This may have an impact on the load bearing capability and fatigue strength of the component.
In general, controlled power tools are not currently available for maintenance work on critical components. Power tools with speed control known in the art have electrical motors as the powering method. As such, the rotational speed of electric motors is usually controlled by limiting the current available to the motor using an electrical motor controller or drive as they are known in the industry. Most electric power tools with drives do not use control methods with closed loop feedback to adjust the speed in real time. This greatly reduces the responsiveness of the power tool when used under variable load by an operator person.
Furthermore, several industrial processes prefer pneumatic tools over electric tools since pneumatic power tools are smaller and more powerfull. However, pneumatic power tools are known for more variability in the rotational speed mainly because of the fluctuations in the supply of compressed air.
The current invention solves this problem by introducing a controlled electro-pneumatic power tool that continuously monitors and adjusts the rotational speed to match the selected speed for the process. This is done using a closed loop feedback control method since the rotational speed needs to be adjusted rapidly and continuously because the force applied on the tool by the operator person will vary constantly. The rotational speed control of pneumatic power tools is intrinsically different from the control of electrical tools. Since air is a compressible gaz, pneumatic power tools have a substantially different power source that necessitates different energy control devices, algorithms, sensors, and power transmission means that will not be obvious to persons with ordinary skills in the art of electrical power tools. Controlled electro-pneumatic power tools with microcontrollers are necessary to use interactive consumable with barcodes or RFID that bring a significant gain in quality, productivity and safety to surface finishing processes.